I needed a frequency reference for tuning up the RS-232 to 100 MHz RF desktop channel adapter elsewhere on this site, when I found this Saronix crystal oscillator in my junk box. A few minutes with AVRStudio produced an ATtiny12 to make a tone – even fewer parts than using an NE-555. With the addition of a transistor to gate the output, I was set to go. Quick and dirty, but it was useful.
The Saronix oscillator has an open emitter output. When the 330 Ohm load resistor on the output is grounded, the RF out of the oscillator increases.
For more detail: 100 MHz RF oscillator using ATtiny12 microcontroller